The present invention relates to electrodeless light sources and more particularly, to a lighting fixture which provides coupling and impedance matching of the power to the lamp. The fixture provides a nominal steady state input impedance of a predetermined value (e.g. 50 or 75.OMEGA.), thereby allowing direct connection via conventional transmission line techniques to a RF power source (e.g. 915 or 2450 MHz).
Microwave electrodeless high intensity discharge (HID) lamps have been coupled to power sources using termination fixtures which are typically large, bulky, shielded coaxial structures. Examples of such fixtures are described in U.S. Pat. Nos. 3,943,403 and 4,002,944. These termination fixtures make the electrodeless lamp undesirable for many applications due to the optical characteristics.
More recently a novel dual ended excitation scheme as taught by Lapatovich in U.S. patent applications Ser. No. 07/523,761 and 07/524,265 has resulted in considerable size and weight reduction of the lamp as well as improved optical characteristics. However this coupling structure as taught by Lapatovich requires an external variable impedance matching means which is bulky and expensive. An example of a variable impedance matching means (e.g. stub tuner) is described in U.S. Pat. No. 4,001,632.
The present invention combines the dual ended excitation scheme with an integral impedance matching network on the same printed circuit board as the balun/applicator as taught in U.S. patent application Ser. No. 07/523,761 and 07/524,265. Since the impedance matching network is integral to the coupling structure, and not separated by connectors and/or coaxial cable, the resulting system performance is less dependent on subtle manufacturing variations. In addition, the tuning network of the present invention is compact, lightweight, inexpensive, and rugged making it a more commercially attractive product than previous attempts at impedance matching.